This study will evaluate clinical and laboratory tests that might be useful in determining if an investigational drug can slow the progression of Niemann-Pick Disease, Type C (NPC), a genetic disorder that results in progressive loss of nervous system function. The study will: 1) look for a clinical or biochemical marker that can be used as a measure of response to treatment, and 2) define the rate of progression of biochemical marker abnormalities in a group of NPC patients who will later be invited to enroll in a treatment trial.

Patients of any age with NPC may be eligible for this study. Participants undergo the following procedures every 6 months during 4- to 5-day admissions at the NIH Clinical Center.

• Medical evaluation, including medical history, physical exam, neurological exam, neuropsychometric evaluation, and blood and urine tests.
• Lumbar puncture (spinal tap): A sample of cerebrospinal fluid (CSF), the fluid that bathes the brain and spinal cord, is obtained for study. After administration of a local anesthetic, a small needle is inserted in the space between the bones in the lower back where the CSF circulates below the spinal cord. A small amount of fluid is collected through the needle.
• Eye exam and eye movement study: The pupils of the eye are dilated to examine the structures of the eyes. For the eye movement study a special contact lens is placed on the eye and the patient looks at a series of target light spots moving on a screen.
• Hearing tests.
• Electroretinography (in patients who can cooperate with the test) to measure the function of the retina. Before the test, the patient's pupils are dilated and an electrode (small silver disk) is taped to the forehead. The patient sits in a dark room for 30 minutes and then a special contact lens is placed on one eye after it has been numbed with drops. The contact lens senses small electrical signals generated by the retina when lights flash. During the ERG recording, the eye is stimulated with flashes of light projected inside a hollow sphere. After the test, a full eye exam is done and photographs of the retina are taken.
• Magnetic resonance imaging (MRI): This test uses a magnetic field and radio waves to produce images of the brain and obtain information about brain chemicals. The patient lies on a table that can slide in and out of the scanner (a narrow cylinder), wearing earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. Patients who cannot remain still in the scanner may be sedated for the test.
• Psychometric testing: Patients complete questionnaires.
• Photographs of the patient may be taken for use in teaching sessions or scientific presentations or publications, with the patient's consent. Patients may be recognizable, but are not identified by name.
• Pregnancy test in all female patients over 10 years of age at the beginning of each admission to the Clinical Center.